Although high-alumina nozzle brick has high fire resistance and corrosion resistance, it is not suitable in some specific cases, mainly in the following aspects:

I. Weak resistance to alkaline slag erosion.

Although the high-alumina nozzle brick has certain corrosion resistance to acidic slag and some alkaline slag, its resistance to alkaline slag is relatively weak because of its small amount of SiO₂. When pouring high manganese steel, stainless steel and other steels that require high corrosion resistance of alkaline slag, the service life of high aluminum nozzle brick may be affected by too fast corrosion.

II. Insufficient thermal conductivity

The thermal conductivity of high-alumina nozzle brick is relatively weak, which may lead to uneven temperature distribution of molten steel during pouring, thus affecting the quality of castings. For example, when pouring special steel with high temperature, the high-alumina nozzle brick may not be able to effectively conduct heat, resulting in the retention time of molten steel at the nozzle for too long, which will lead to problems such as nodulation.

III. Limited thermal shock stability

Although high-alumina nozzle brick has certain thermal shock resistance, its performance may still be affected under frequent quenching and heating conditions. For example, in the process of continuous casting, the nozzle brick needs to bear the impact of high-temperature molten steel and the rapid cooling of cooling water frequently, and the high-aluminum nozzle brick may crack or peel off in this case.

IV. Not suitable for high erosion environment

In some extreme corrosive environments, such as high oxidizing atmosphere or high scouring force of molten steel flow, the performance of high aluminum nozzle brick may not be as good as that of aluminum-carbon or zirconium nozzle brick. For example, in the slide gate system of continuous casting tundish, due to the high-speed flow of molten steel and frequent switching operation, high-alumina nozzle bricks may be rapidly worn by scouring.

V. Cost and cost performance

The price of high-alumina nozzle brick is relatively high, and its cost limits its wide application to some extent. In some occasions where the performance of refractories is low, the use of high-alumina nozzle bricks may cause unnecessary cost waste.

VI. Not suitable for long-term high temperature stay.

When the molten steel stays in the ladle for a long time, the high-alumina nozzle brick may be damaged rapidly due to long-term high-temperature erosion. In this case, it is more suitable to use materials with better thermal conductivity and stronger corrosion resistance, such as magnesia-carbon or zirconium nozzle bricks.

VII. Summary

Although high-alumina nozzle brick has high refractoriness and corrosion resistance, it has some limitations in alkali slag corrosion resistance, thermal conductivity, thermal shock stability and cost. When selecting nozzle brick, it is necessary to comprehensively consider the specific steel grade, pouring technology and use environment to ensure that its performance can meet the actual demand.